1. Field of the Invention
The present invention relates to transferring data packets across a network. More specifically, the present invention relates to a method and an apparatus for facilitating instant failover during packet routing by employing a flooding protocol to send packets on all possible paths between a source and a destination.
2. Related Art
Fault tolerant networks commonly provide redundant communication links between machines that are communicating with each other. If one link fails, the system will ideally failover instantly to another link.
However, traditional routing techniques take a significant amount of time to detect and route around a failure. Consequently, these traditional routing techniques will not work for systems that require instant failover.
Instead of these traditional techniques, a flooding protocol can be used that sends all packets everywhere. This is typically accomplished by configuring intermediate nodes between a source and a destination so that they forward a packet to all neighboring nodes except the node from which the packet was received. A flooding protocol has the property that if there is any path between the source and the destination, the packet will be delivered. It does not depend on intermediate routers having consistent forwarding tables or knowing the topology of the network.
In theory, a flooding protocol can create an exponential number of packets, which can seriously degrade network performance. However, a “link-state routing protocol” uses flooding with reasonable efficiency for distributing routing information throughout a network. The reason the link-state routing protocol can be efficient is that each router stores a link state packet (LSP) with the highest sequence number from each source. When a router receives an LSP from a source, it checks its database and only stores and floods the LSP if the sequence number is higher than the one in the database for the source. In this way, a router will not reflood the same packet or an older packet.
Unfortunately, the same technique will not work for data packets because routers do not store data packets and consequently cannot recognize duplicates. Moreover, data packets may arrive out-of-order, and unlike LSPs, where only the most recently generated LSP is of interest, a large number of data packets may be en route at any one time, and all of these data packets are of interest.
What is needed is a method and apparatus for facilitating flooding of data packets without seriously degrading network performance.